Interpretive Summary: In spite of the interest in grazing impacts on riparian systems, there is limited information on root response of riparian sedges to grazing. We evaluated field use of an ingrowth core technique using vacuum sampling for estimating riparian sedge root production. Estimates of root production averaged 356.7 (+/-20.6) g/m2 and the technique proved to be a workable solution for sampling in seasonally inundated environments. Our technique provides researchers with a practical method for determining below ground plant production in riparian environments.

Technical Abstract:
Below-ground plant biomass plays a critical role in the maintenance of riparian ecosystems. Despite this importance, below-ground dynamics of riparian plant species are not commonly investigated, in part due to difficulties of sampling in a below-ground riparian environment. We investigated the field utility of a root ingrowth sampling technique for measuring annual root production. We established 4 streamside sampling sites in southeastern Oregon, and randomly located 4 plots within each site. In each plot we established two 7.6 cm-diameter sand filled ingrowth cores in September of 2004. In September of 2005 we harvested the cores using a vacuum sampling technique in which a 5.1-cm diameter camphored PVC casing was driven into the center of the root core and sand and root materials were suctioned out. Root length density was determined by computer image analysis and roots were dried and weighed to determine production by weight. Results indicate that root length density averaged 7.2 (+/-0.7) cm/cm3 across sites and annual root production by weight was 356.7 (+/-20.6) g/m2. Production estimates by weight are consistent with previous work reported in the literature. Our sampling technique proved to be a practical solution for root sampling in riparian environments and helps overcome some of the difficulties in sequential coring of saturated soils. Our technique may be advantageous to using mesh ingrowth cylinders because we use sharpened PVC to cleanly cut the roots growing into the core prior to harvest. Use of any ingrowth core technique to estimate root production can potentially bias production estimates due to the artificial, root-free environment of the core. However, these biases should be consistent across sites making ingrowth cores useful for determining differences between manipulative treatments.